Successful management of diabetes in youth is heavily dependent upon family adaptation to the affective, behavioral, and cognitive demands imposed by the disease. During pre and early adolescence, transition in responsibility for diabetes management, along with normal physiological and psychological developmental changes, create an especially challenging situation. Although many youths and parents negotiate this transition effectively, it is also a period when many other youths take costly, self-destructive paths resulting in preventable health care costs and psychological suffering in the short-term and accelerated onset and progression of long-term complications of the disease. Studies suggest that poor adaptation to diabetes during adolescence is likely to persist into early adulthood, accelerating the risks of long-term medical complications. Research to date suggest that adherence, quality of life, and glycemic control could be enhanced if behavioral interventions were routinely implemented as part of standard care. Yet there are many barriers to the translation of these interventions into routine clinical practice, including cost, access, third party coverage, availability of qualified clinicians, convenience, social stigma, and other such variables. A multi-component behavioral intervention that integrates psychological principles into medical management of diabetes is likely to enhance family management of diabetes during early adolescence in a practical, cost-effective and lasting manner. The goal of this multi-site study was to assess the efficacy of a clinic-integrated behavioral intervention for youth with type 1 diabetes and their parents. The study employed a randomized experimental design in which youth-parent dyads attending one of four clinical sites were stratified by degree of glycemic control and randomized to receive either standard care or a clinic-integrated behavioral intervention. The intervention was based on both individual and family system theoretical perspectives, including social cognitive theory, self-regulation, and authoritative parenting. It was designed to provide experiential training for families in the use of a problem solving approach to promote improved parent-child teamwork and more effective problem-solving skills for diabetes management. The intervention was designed to be applicable to the broad population of youth with diabetes and their families, flexibly implemented and tailored to the varying needs of families, and delivered at a low intensity over time to meet the changing needs and roles of families during the period in which responsibility for diabetes management typically undergoes transition. A combination of in-person assessments, telephone assessments, and in-clinic data collection were utilized to assess glycemic control, adherence, quality of life, psychological status, and hypothesized mediators of these outcomes Several pilot studies informed this clinical trial. A longitudinal observational study, Developmental Influences on Management of Type 1 Diabetes, examined the influence of family, social, and behavioral variables on diabetes self-management behaviors with a particular focus on adolescent developmental transitions. A pilot intervention study, the Diabetes Personal Trainer Study, assessed the effectiveness of an individualized problem-solving approach, guided by principles of motivational interviewing and applied behavior analysis, and implemented by specially-trained undergraduate and graduate students, who served as diabetes personal trainers. A pilot study of an abbreviated form of the specific intervention approach used in the multi-site clinical trial assessed the feasibility of the study design and intervention approach.